A novel approach to full-mouth rehabilitation of dentinogenesis imperfecta type II: Case series with review of literature

Rationale: Dentinogenesis imperfecta (DI) is an autosomal-dominant disorder. The most common clinical manifestations, including obliterated tooth tissues and severe tooth wear, usually lead to tooth extractions. It remains a great challenge for dentists to preserve the residual tooth tissue and establish the esthetics and occlusion of dentitions. Patients concerns: 25-year-old twin sisters, who had suffered from dentinogenesis imperfecta type II for more than 10 years, presented with continuous tooth wear and discomfort from wearing a removable partial denture for more than 3 years. Diagnosis: Intraoral examination showed extensive tooth wear with enamel exfoliation and typical amber-brown color with an opalescent discoloration. Their panoramic radiographs revealed completely obliterated tooth tissues and severe tooth wear. Interventions and outcomes: The dentitions were restored with post-and-core crowns and pin lays after preparing root post paths and pin holes guided by computer-aided design/computer-aided manufacturing (CAD/CAM) procedures, resulting in a successful repair. Lessons: Severe tooth wear and tooth tissue obliteration are typical clinical manifestations in DI-affected dentitions, increasing the complexity and difficulty in dental restorations. Early diagnosis and appropriate treatments are essential to achieve a favorable prognosis. CAD/CAM procedures, permitting accurate and effective treatment, possess promising potential in the treatment of DI-affected dentitions.


Introduction
Dentinogenesis imperfecta (DI) is a localized mesodermal dysplasia that is characterized by dentin hypomineralization and abnormal dentin structure. [1,2]Besides, it is inherited in an autosomal dominant pattern with high penetrance and low mutation rate. [3]The incidence of DI has been reported to be between 1 in 6000 and 1 in 8000, and DI type II was reported to have a prevalence of 0.0022% in a Swedish study. [4,5][7] Shields classification system categorizes DI into 3 types. [8]DI type I is associated with osteogenesis imperfecta. [4]DI type II possesses many clinical and radiographic features similar to DI type I without osteogenesis imperfecta. [4,9]Type-III, a phenotype found in a tri-racial population in Maryland and Washington DC, is characterized by large pulp chambers. [4]Clinically, the affected teeth are discolored, ranging from opalescent blue-gray to dark yellow-brown. [10]][13] Structural defects are characterized by bulbous crowns, cervical constrictions, small pulp chambers, and partially or completely obliterated root canals. [7]arly diagnosis and appropriate treatments are essential to achieve a favorable prognosis.The treatment of DI is often complicated and case-dependent.Prompt interventions are essential Y-ZZ and X-TJ contributed equally to this work.

The study was supported by National Natural Science Foundation of China (81970982).
The authors have no conflicts of interest to disclose.
The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.a  to protect primary and mixed dentitions with metallic restorations.Generally, the treatment aims to preserve the tooth tissues, prevent further loss of the vertical dimension of occlusion, and restore tooth functions and esthetics. [14]But when the severe tooth wear has occurred in permanent dentition, the rehabilitation could be complex and unpredictable. [15]This scenario requires other restorative methods to achieve a predictable rehabilitation.
Recent advances in computer-aided design/computer-aided manufacturing (CAD/CAM) technology have generated a revolution in modern dentistry, enabling more accurate treatment and surgery.CAD/CAM templates have been applied in various fields, such as implant surgery, guided endodontics, orthognathic surgery and so on. [15]The templates permit the personalized design of dental appliances, simplify the implementation of complex procedures with less error, and overcome the limitations in freehand operation. [15]he purpose of our clinical reports was to present tooth restorations in 2 cases of twin sisters diagnosed with DI type II, with the aid of CAD/CAM templates (Soft tissue -Supported Guide, 6D-Dental Medical Technology Co., Ltd, Hangzhou, China) to permit the accurate preparation of root post paths and pin holes in obliterated tooth tissues, facilitating the subsequent restoration of metal-ceramic post-and-core crowns and pin lays.A review of the state-of-the-art of the treatments in DI-affected dentitions during different periods with typical clinical manifestations was performed.

Case presentation
The 25-year-old twin sisters, with the diagnosis of DI type II for more than 10 years, visited the Stomatology Hospital, School of Stomatology, Zhejiang University School of Medicine.They mainly complained about the consecutive tooth wear, and uncomfortableness of removable partial dentures that had been worn for more than 3 years.They both have not reported any other systemic diseases.The family medical history revealed that their father, paternal grandmother and one of their father's siblings had similar dental symptoms (Fig. 1).Extraoral examination revealed that the patients had no perceptible loss of occlusal vertical dimension without pain and clicking of temporomandibular joint.Intraoral examination showed extensive tooth wear with enamel exfoliation and typical amber-brown color with an opalescent discoloration (Fig. 2A-F).Their panoramic radiographs revealed complete obliterated tooth tissues (Fig. 2G, H).Periapical lesions on the tooth #16 were detected in the elder sister (Fig. 2H).The patient involved in the study have signed a written informed consent that the health-related data would be used for research purposes and photographs would be published in this way.This study was approved by the Institutional Ethic Board of the Affiliated Stomatology Hospital, Zhejiang University School of Medicine, Hangzhou, China (No. 2020-16).

Treatment plan
The patient consent form was taken.Restorative options, including implant-supported restoration, and post-and-core crowns and pin lays restoration, were proposed.The latter was accepted.We reminded them that a deep bite might occur in anterior region, an orthodontic treatment was better to be performed, but they refused because of its long therapeutic time and high costs.According to the treatment plans, routine oral hygiene instructions were given and ultrasonic scaling was performed firstly.CAD/CAM templates were planned to guide the preparation of root post paths and pin holes in obliterated tooth tissues.The posterior teeth were restored with pin lays, and anterior teeth were restored with post-and-core 2-unit crowns.All-ceramic restorations were recommended but metal-ceramic ones were finally chosen because of their limited financial resources.For the elder sister, teeth #31 and 41 were replaced with 2 implants because the roots were too short.The tooth #16 with periapical lesions was left untreated since endodontic treatment was difficult to conduct due to the complete obliteration of tooth tissues, and the extraction may be performed if the lesions progressed.

Building the CAD/CAM template
A high-resolution cone-beam computed tomography (CBCT) scan was taken using the NewTom VGi (NewTom, Verona, Italy), operating at 110 kVp, 1.64 mA, 3.6 seconds with a FOV of 15 × 12 cm and voxel size 0.3 mm.The design of the root post paths and pin holes was determined according to the diameter and length of each root obtained from the CBCT data (Fig. 3A).Post paths for anterior teeth were designed with a diameter of 0.9 mm in the middle of the root leaving 1 mm of root wall thickness and 3 mm to the apical point.Pin holes were designed with 2 pins for premolars leaving 2 mm from the buccal or lingual side in middle line from the mesiodistal view, and 3 or 4 pins for the molars leaving 2 mm from the axial walls.Pin holes should be parallel to each other in the same tooth with a diameter of 0.6 mm and a depth of 2 mm.The post drill (ParaPost, Ref.: P423; Coltene/Whaledent AG, Altstätten, Switzerland) for root post path preparation and the pin drill (Self-threading screw, Ref.: K11-60; Westlake Biological Materials Co., Ltd, Hangzhou, China) for pin hole preparation were used in this study (Fig. 3B).After impressions of the upper and lower dentitions were taken using silicone rubber impression materials (3M ESPE Express, St. Paul, MN), stone casts were obtained, and scanned using an optical scanner (D700, 3Shape, Copenhagen, Denmark) with an accuracy of 20 µm.Image datasets including CBCT data and digital impression data were uploaded to design software (Version2.0,6D-Dental Medical Technology Co., Ltd, Hangzhou, China), and their images matched based on radiopaque dental structures.The superimposition of the drills was positioned in the middle of the designed roots (Fig. 3C).Guiding sleeves (0.9 mm internal diameter, 1.7 mm external diameter for post paths; 0.6 mm internal diameter, 1.4 mm external diameter for pin holes) were customized for each drill, and templates were designed (Fig. 3D).Data was exported as STL files and printed using a 3D printer (Objet 350 Connex3, Stratasys), and the designed sleeves were incorporated into the templates (Fig. 3E).

Prosthodontic treatment
The templates were positioned on the dentition and fitness was checked (Fig. 4A).The drills were used to prepare root post paths and pin holes until the end of the drill shafts touched the sleeves.One-step impression technique was used with silicone rubber impression materials for anterior post paths with dentition, and after that, a stone cast was obtained.Upper and lower casts were mounted on an articulator according to the occlusal relationship record.Post-and-cores of anterior teeth were fabricated, tried in and cemented with glass ionomer cement (GIC) (GC Fuji I, Japan).The finishing margin was prepared with a circumferential chamfer of approximately 0.5 mm width at 0.5 mm of subgingival.An orthodontic round wire (0.020'', F810-35, Westlake Biological Materials Co., Ltd, Hangzhou, China) was bent into approximately 3 mm pin with a small loop, which served as impression auxiliary pins, and were sandblasted before use.Gingival retraction with the double cord technique (#000 and #1, Ultrapak, Ultradent Products, Inc., UT) was used in this study.Auxiliary pins were inserted into pin holes immediately after the light body was injected over pin holes and directly into post paths using a modified No. 9 needle (Fig. 4B).One-step impression technique was used for both upper and lower dentitions, and their casts were obtained.Routine occlusal relationships were recorded and metal-ceramic pin lays and crowns were fabricated, tried in, marginal adaption checked in place, and occlusal adjustment was performed.The 2-unit crowns of anterior teeth were finally cemented with the GIC.The full-mouth rehabilitation for the younger sister was finished as above mentioned.But the treatment for the elder sister was more complex.Two dental implants (SLA, bone level, Ref.: 021.2514,Institution Straumann AG, Basel, Switzerland) were inserted in the site of teeth #31 and 41 after bone grafting, which used artificial bone powders and collagen membranes (bone powder: Bio-Oss, Geistlich, Switzerland; collagen membrane: Bio-Gide, Geistlich, Switzerland).Two models of each jaw were made and a check bite was performed.The models were mounted in an articulator and scanned using an optical scanner.Afterwards, maxillary anterior transitional crowns and a mandibular implant-supported transitional cantilever bridge were designed and fabricated with CAD/CAM technologies.The transitional dentures and definitive restorations on premolars in both jaws were subsequently restored and 3 months later, transitional dentures were replaced with definitive ones.

Clinical outcomes
Posttreatment photographs showed that the definitive restorations were satisfactory, and the patients were satisfied with the treatment results (Fig. 5).The patients were recalled at 3, 6 and 12 months in the first year, and once a year afterwards.For the younger sister, the 2-unit crowns of the teeth #11 and 21 were dislodged at 37 months.The dislodged crowns were recemented.The pin lay of the tooth #14 was broken at 40 months due to the direct chewing of hickory.The pin lay was refabricated and cemented.For the elder sister, the post-and-core crowns of the teeth #11 and 21 were dislodged at 20 months.The 2-unit crowns of the teeth #12 and 13, 22 and 23 were dislodged at 23 months.The fixed prothesis were cleaned and re-cemented.

Literature search
A literature search was conducted on the treatment of DI-affected dentitions with typical clinical manifestations, especially tooth wear and/or tooth tissue obliteration.The electronic database Web of Science were searched from inception to 31st January 2023 using the following MeSH terms: "dentinogenesis imperfecta", "treatment", and "therapy".It was supplemented by manual searches in the reference lists of the relevant articles.The search retrieved 300 results.Different types of peer-reviewed publications, only in the English language, were screened as follows: indexed reviews, case reports and case series.After screening the title, abstract and full-text, 92 relevant full-length articles were included.Among them, 28 cases that reported the treatment of DI-affected dentitions in different periods were selected, summarized and listed in Tables 1-3.

Discussion
DI is a genetic disorder that affects the structural integrity of the dentin. [10]The most common features of DI include tooth wear and obliterated tooth tissues, which account for the increasing complexity and unpredictability of the restorations in DI-affected dentitions.In our clinical reports, the patients were examined with typical clinical manifestations of DI type II, tooth extractions and implant-supported fixed or removable prostheses were proposed as an alternative.But full-mouth rehabilitation was finally achieved assisted with CAD/CAM procedures, preserving the residual tooth tissues with acceptable esthetics and functions.Our reports add new elements to the literature regarding the dental management of DI patients.In order to identify the treatments in different periods and conditions of DI, a literature review was required.
Early identification and preventive interventions are critical for DI children to intercept tooth wear and prevent pulp damage. [3,18,22]Otherwise, the unrestorable deterioration of dentitions may affect the normal growth of facial bones and temporomandibular joint, leading to an unesthetic appearance and  causing psychological problems. [15]Maintenance of good oral hygiene, pit and fissure sealing and topical fluoride application as effective early preventive approaches are strongly recommended. [22]Early restoration of primary molars and permanent first molars during mixed dentition with stainless steel crowns is an effective method to prevent tooth wear. [3,23,24]When the children reach adulthood, stainless steel crowns can be replaced with full crowns. [25]Primary anterior teeth are restored with aesthetic preformed pediatric crowns such as resin composite strip crowns, polycarbonate crowns and zirconia crowns. [26,27]owever, insufficient evidence support any method or particular material for the primary anterior teeth. [28]Permanent anterior teeth should be restored with composite as soon as eruption starts to reduce tooth wear, and can also be protected with celluloid strip crowns or polycarbonate crowns, and porcelain crowns at a later stage. [24]Teeth that cannot be restored with crowns can be restored with overlay dentures on the residual crowns and roots. [29]rious approaches for managing DI-affected permanent dentitions have been documented.Routine restorative techniques including composite restorations and veneers might be used for the dentitions without enamel fracture or extensive wear. [30,31]he full-coverage crowns are the preferred choice for the teeth with extensive tooth wear. [30,32]However, the worn teeth are always unable to provide sufficient retention for crowns restoration.Soliman S et al [13] used self-threading parapulpal retentive pins in combination with composite resin buildup cores, though they do not possess stronger retention than conventional posts and cores.Crown lengthening procedures on teeth without bulbous shape or short roots to obtain sufficient clinical crown height is an another approach to obtain sufficient retention for crown restorations. [14,31,33,34]Splinted crowns are sometimes recommended to reduce the risk of individual root fracture. [35]ith the development of technology, indirect adhesive restorations can replace crowns in minimal invasive preparations on DI-affected teeth.Indirect composite resin overlays have been Table 1 The summary of DI-affected primary dentitions with typical clinical manifestations and the treatments.

Clinical and radiographic manifestations
Treatment Follow-up Sapir S et al, 2001 [3] -Israel An The severity of tooth wear was rated with the Tooth wear Index proposed by Smith BG and Knight JK in 1984 45 , estimated by the authors depending on the provided text and image information.The acronym "FPD" represents "fixed partial denture", "P" represents "pontic", "OP" represents "operation", "VDO" represents "vertical dimension of occlusion", "SSC" represents "stainless steel crown", "GIC" represents "glass ionomer cement".DI = dentinogenesis imperfect, SSCs = stainless steel crowns.

Table 2
The summary of DI-affected mixed dentitions with typical clinical manifestations and the treatments.

Author(s)country
Age and gender Clinical and radiographic manifestations Treatment Follow-up Delgado AC et al, 2008 [18]  CAD/CAM = computer-aided design/computer-aided manufacturing, DI = dentinogenesis imperfect, SSCs = stainless steel crowns, VDO = vertical dimension of occlusion.

Zhang et al. • Medicine (2024) 103:4 Medicine
Table 3 The summary of DI-affected permanent dentitions with typical clinical manifestations and the treatments.

Age and gender
Clinical and radiographic manifestations Treatment Follow-up Licht WS et al, 1980 [36]  The patient showed a pleasing facial appearance after finishing the treatment.
Seymour DW et al, 2012 [37] -UK A 48-yrold woman Root canal obliteration; FPD: #13P 12  used for DI patients without adhesive failure for 13 years. [31]hen the tooth loss occur, the dentitions could be restored with fixed partial dentures and implant-supported crowns or bridges. [32,33,36,37]However, fixed partial dentures might exert extreme stress on the teeth and increase the risks of root fractures. [36]The implant-supported fixed or removable dentures is a predictable approach, but the cost is expensive and the implant placement should be prudently planned. [14]Overdenture is a common removable denture with the underlying residual tooth tissues restored with copings. [36]It is a comparatively cheaper prosthesis, however, it might hamper oral hygiene. [7,14,38]he most recent cases reports focus on the application of digital workflows and multidisciplinary treatments in DI-affected dentitions.Fan F et al [34] used digital smile design to design the esthetics of the anterior teeth, which were severely worn with unesthetic appearance.A multidisciplinary treatment protocol focusing on prosthodontics proved highly effective in the esthetic restorations.Shi S et al [30] used digital techniques including digital smile design, the ARCUSdigma axiograph and CAD/ CAM to achieve accurate occlusion and improve the efficacy of esthetic rehabilitation in DI.CAD/CAM technology has been reported to assist in the fabrication of monolithic prostheses with reduced thickness for a moderately cooperative DI child with severe tooth wear. [20]Another case reported that a minimally invasive and effective rehabilitation in a DI child was achieved through digital workflows, including intraoral scanning and individual crowns manufacturing via CAD/CAM. [30]zpiazu-Flores FX et al presented the interdisciplinary management of a DI patient.CAD-CAM procedures were applied to fabricate devices that aided planning, assisted intermaxillary fixation and implant placement, and enabled the accurate establishment of the definitive full-arch prostheses.
In our clinical reports, the 2 patients were examined with severely affected dentitions, requiring complex reconstructions involving advanced prosthetic treatments.The CAD/CAM procedures made it feasible.In our cases, root post paths and pin holes were accurately prepared in obliterated pulp chambers and root canals assisted with the CAD/CAM templates.Other than high accuracy, minimally invasive preparation, reduced chair time and decreased technique sensitivity were also achieved.However, without the templates, the preparation could be difficult and unpredictable, and root perforation may occur, which could lead to tooth extraction.This is because the roots are thin and the preparation direction of paths and holes is difficult to control using the free hand.With the subsequent restoration of metal-ceramic post-and-core crowns and pin lays, maximizing residual tooth hard tissues preservation and full-mouth rehabilitation were both achieved.Generally.CAD/CAM templates have been widely used in dentistry, but they have not been reported to guide the accurate root post paths and pin holes preparation in fully obliterated tooth tissues in DI patients.
The treatment plans including tooth extractions with implants replacement were proposed at first.But the patients urged to preserve their natural teeth even for a short time, and the high costs of implant restorations were unaffordable to them.Therefore, they chose the traditional post-and-core crowns and pin lays restorations.The root lengths of anterior teeth were basically sufficient for post-and-core restorations Ayyildiz S et al, 2013 [44] -Turkey An Azpiazu-Flores FX et al, 2022 [15] -USA  but insufficient for crown lengthening procedures, therefore, it was not performed.Two-unit crowns were used in anterior region to reduce the risk of individual root fracture, because of the occurrence of a moderate deep bite.Pin lays were used in posterior teeth in order to enhance the mechanical retention force.Overlays or occlusal veneers were not used because of the insufficient adhesion between the restorations and malformed tooth tissue.Although the pins were thin and short, we didn't find any fracture under normal conditions during the 3-year follow-up, expect a fracture in the 40 th month associated with chewing of hard hickory.The restorations were made in metal-ceramic rather than all-ceramic because of the high costs of the latter, although the latter could provide better esthetics.Follow-up studies in the cases revealed several problems.Prosthesis dislodgement occurred severally in both patients during the 3-year follow-up period, which should be attributed to the severe tooth wear of their dentitions, and the decrease in bond strength between the cement and malformed hard tissue. [13]The GIC rather than resin-based cement was used, because both gained similar bond performance for cast restorations in DI. [14] The prothesis dislodgement mainly occurred in the anterior region, which might have resulted from occlusal interference by a moderate deep bite.Orthodontic interventions could effectively eliminate the deep bite, but were not considered because of long therapeutic time and high costs.
Clinically, clinicians always provide the best treatment plans for patients, but usually, they are not accepted by patients, limited by the costs, patients desires and clinical resources.So individual treatments were required.In our cases, some problems kept its existence in the therapeutic cycle, but our treatment seemed to be the best choice considering all the factors.Furthermore, CAD-CAM templates possess promising potential in the treatment of DI-affected dentitions.

Conclusion
DI is an autosomal dominant condition with complex manifestations that increases the difficulty and predictability of the treatment.Early diagnosis and appropriate treatments are essential to achieve a favorable prognosis.Individual treatments are required to achieve satisfactory esthetics and functions.In our cases, CAD/CAM templates guided the accurate preparation of root post paths and pin holes in obliterated tooth tissues, facilitate the full-mouth rehabilitation in 2 patients with acceptable results.We conclude that CAD/CAM technology could be recognized as a blueprint in oral rehabilitation.

Figure 2 .
Figure 2. Pretreatment intraoral views and panoramic radiographs of the younger sister (panels A-C, G) and the elder one (panels D-F, H).The teeth showed severe tooth wear and dental caries indicating anterior open bite (panels A-F).For the elder sister, the teeth #16, 17, 36, and 37 were restored with full metal crowns, and the teeth # 46 and 47 were restored with acrylic resin veneer metal crowns (panels E, F), while preserving posterior occlusal contact relationships and VDO (panel D).Radiographs showed that all teeth have completely obliterated pulp chambers and root canals (panels G, H).VDO = vertical dimension of occlusion.

Figure 3 .
Figure 3.The brief procedures of an upper CAD/CAM template construction.(A) Two pin holes were designed in a lower premolar based on the CBCT data.(B) The drills for preparation (left: for pin holes, 0.6 mm in diameter; right: for root post paths, 0.9 mm in diameter).(C) Guiding sleeves were deigned after the CBCT data and digital impression data were matched based on radiopaque structures.(D) The digital template was finally designed.(E) The template was printed with the designed sleeves incorporated.CAD/CAM = computer-aided design/computer-aided manufacturing, CBCT = cone-beam computed tomography.

Figure 4 .
Figure 4. (A) The drills used (left: for pin holes preparation, 0.6 mm in diameter; right: for post paths preparation, 0.9 mm in diameter).(B) The maxillary CAD/CAM template.(C) Positioning of the template on the dentition.(D) Impression making: the impression auxiliary pin was insert into pin holes (shown in the upper right-hand corner) while injecting the light body over pin holes.CAD/CAM = computer-aided design/computer-aided manufacturing.
Stomatology Hospital, School of Stomatology, Zhejiang University School of Medicine, Zhejiang Provincial Clinical Research Center for Oral Diseases, Key Laboratory of Oral Biomedical Research of Zhejiang Province, Cancer Center of Zhejiang University, Engineering Research Center of Oral Biomaterials and Devices of Zhejiang Province, Hangzhou, China, bThe Fourth Affiliated Hospital, Zhejiang University School of Medicine, Yiwu, China, c 6D Dental Tech CO., Ltd, Hangzhou, China.